Chiff circuits for electronic organs

ABSTRACT

In a keyed-photocell electronic organ, two (or more) photocells are keyed with a single, make-break key switch via two (or more) respective RC keying or envelope-control circuits, one of which provides a transient keying pulse to a photocell in order to produce a chiff tone component. The chiff keying circuit includes a series capacitor, the output terminal of which is always clamped to ground by a diode circuit except for a short interval after the key switch is closed during which the level at the output terminal initially jumps and then falls off as the series capacitor charges.

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break key envelope- IRP. CELL 51 5/1962 Markowitz................... 3,291,886 12/1966 Tinker.......................... 7/1967 Brombaugh..................

2/1970 Cunningham............:::.

Primary Examiner-D. F. Duggan ORCH. FLUTE a jcistucg) 4'cELL 53 Z25 TE 1(( 2. wc ii tc 94 2% 3,333,042 3,476,866 11/1969 Cunningham..... 3,495,021

Assistant Examiner-U. Weldon AtrorneysW. H. Breunig and Hurvitz & Rose ABSTRACT: In a keyed-photocell electronic organ, two (or more) photocells are keyed with a single, makeswitch via two (or more) respective RC keying or Glob 3/06 control circuits, one of which provides a transient keying pulse 84/101, to a photocell in order to produce a chiff tone component. The chiff keying circuit includes a series capacitor, the output terminal of which is always clamped to ground by a diode circuit except for a short interval after the key switch is closed during which the level at the output terminal initially jumps 84/1 18 and then falls off as the series capacitor charges.

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References Cited UNITED STATES PATENTS 3/1962 Jones et a1. CKC. (CM) William C. Wayne, Jr. South Fort Mitchell, Ky.; Albert Meyer, Cincinnati, Ohio [21] Appl. No. 21,815

Mar. 23, 1970 [45] Patented Nov. 2, 1971 D. H. Baldwin Company Cincinnati, Ohio Assignee 8 Claims, 4 Drawing Figs.

United States Patent [72] Inventors [22] Filed [54] CHIFF CIRCUITS FOR ELECTRONIC ORGANS [50] FieldofSearch............................................

FATENTEUNUVZ IHYI 3, 17,503

sum 10F 2 \NVENTURS ULHLUHM C. UURYNE l q ALBERT MEYER Mgr- [ATTORNEYS BACKGROUND OF THE INVENTION The present invention relates to producing chiff components in electronic organs andmore particularly, in photoelectric organs of the type described in US. Pat. No. 3,023,657.

U.S. Pat. Nos. 3,989,886 (to Markowitz), 3,333,042 (to Brombaugh) and 3,330,223 (to Wayne) disclose three different techniques for producing chiff" in electronic organs. Chifi'is the common term applied to audible starting transients in the tones of certain organ pipes. Also, Markowitz, in U.S. Pat. No. 3,037,413 discloses a circuit in which direct current is fed via a single make-break key switch to both a first keyedon electronic oscillator providing the steady-state component of a tone and a second keyed-on electronic oscillator to provide a chifl' component for that tone. Further, a copending US. Pat. application, of Daniel W. Martin, Ser. No. 21,811 filed Mar. 23, 1970, and assigned to the same assignee as the present application, discloses, in the context of a photoelectric organ, simultaneous keying, via a single key switch, of a slow time constant circuit connected to key slow-starting tones of one timbre and a fast time-constant circuit connected to key fast-starting tones of another timbre. The present invention, with particular reference to a photoelectric organ of the kelled-photocell type disclosed and claimed in U.S. Pat. No. 3,023,657 to Jones and Love, employs a particular chiff-envelope-control network to actuate, via a single key switch and a DC source, a photocell corresponding to a chifi' component at the same time that DC is keyed to a steady-state tone envelope-control network connected to a photocell corresponding to a steady-state tone signal. The prior art is silent on the subject of chit't' in photoelectric organs of the type disclosed by Jones and Love.

SUMMARY OF THE INVENTION One means for producing steady-state tone signals usually accompanied by a chiff component, and one means for producing tone signals corresponding to the chiff component desired to precede the steady-state tone are simultaneously actuated by a single key switch via separate envelope control networks having rise times and decay times corresponding to the steady-state and chiff components desired. The specific chiff tone-envelope-control network receives keyed DC voltage from a first supply across a resistive voltage divider having across a portion thereof a pair of capacitors in series, there being across one of the capacitors output connections and a diode poled oppositely to said DC voltage. Across the diode is a resistor in series with a second DC supply, the latter being poled for conduction of the diode. With no DC voltage keyed from the first source, the output connection is clamped to ground by the diode in series with the resistor and second supply. When keyed, the output connection rises substantially immediately to a predetermined level and decays quickly as the capacitors charge, the limit of the decay being determined by the clamping action of the diode. The output connection remains at zero when voltage from the first supply is removed because of the clamping action; however capacitor discharge is effected at this time.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a broken, diagrammatic (and partly schematic) view of the main components of the type photoelectric organ to which this invention applies;

FIG. 2 is a part-block, part-schematic circuit diagram of a keying system for a photoelectric organ in accordance with this invention;

FIG. 3 is a schematic circuit diagram illustrating the details of the system of FIG. 2; and

FIG. 4 is a plan view of a portion of a photocell array as employed with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Referring to FIG. 1 of the accompanying drawings, the Jones-type photoelectric organ, to which this invention is particularly applicable, comprises a light source (not shown), radiation from which falls upon a rotating pitch disc 1. Concentric circles of transparent slots 3, (a circle for each musical pitch) cause apparent moving beams of light to scan waveform patterns, as at 5 and 7, in a stationary disc 21. Patterns 5, 7 may be either of variable-area or variable-density character, as known in the art, so as to determine the timbre of the tones produced. The modulated light falls upon a schematically illustrated photocell array 11 on stationary plate 11a, the array comprising a series of split photocells formed, for example, between a keying electrode 13 and two collecting electrodes 15 and 17, across which is deposited a layer 19 of photosensitive material, for example, lead sulfide. The physical layout of a photocell array is further described hereinafter in connection with FIG. 4, while the details of operation of the present invention are discussed with reference to FIGS. 2 AND 3.

Referring now to FIG. 2, a simple, make-break key switch 2 having a pair of contacts actuated by a playing key 4 of a conventional keyboard (not shown), switches direct current from a source 8+ to a fast keying circuit 6 at the same time as it switches 13+ to a slow keying circuit 8. Multiple output connections of fast keying circuit 6 are directed to one photocell electrode (13 in FIG. 1) in each of plural arrays of the type described in FIGS. 1 and 4, the groups being indicated in FIG. 2 on disc 11a as 8' Reed, 4' Reed, 2' Flute, and l Flute. The multiple output leads from the slow keying circuit 8 are directed to plural photocell arrays indicated as 16' Bourdon, 4' Flute and 8' Flute. Thus, from a single key switch 2, the photocells for both relatively fast-starting tones and relatively slow-starting tones are energized by DC from the source B+. This arrangement forms the subject matter of a copending U.S. Pat. application, in the name of D. W. Martin, Ser. No. 21,81 1, filed Mar. 23, 1970 and assigned to the same assignee as the present application. In the interest of simplicity of FIG. 2, the light source, pitch disc 1, waveform disc 21 and output system for the photocells are omitted. FIG. 2 also contains a chiff keying circuit 9, the nature of which forms the subject matter of the present invention.

Reference is now made to FIG. 3 of the drawing, wherein are illustrated the details of a keying system for two adjacent semitones of a keyboard (for example, a Swell manual), in accordance with the invention. A playing key 10 of a conventional keyboard (not shown), corresponding to note C, (mid dle C at 8 pitch) selectively actuates a key switch 12 having a connection to a DC source 14 and a connection to a click suppressing resistor 16 of low resistance, the latter in turn being connected to a plurality of keying or time constant circuits illustrated as CKC (C FKC (C,) and SKC (C representing respectively chiff keying circuit, fast keying circuit and slow keying circuit, for the note C Dashed lines enclose those elements of the several keying circuits which can be considered part of the keying circuits themselves. The slow keying circuit SKC (C is comprised of a diode 23 polarized to conduct current from source 14 and feeding a shunt resistor 18 and series resistor 20, with a shunt capacitor 22. A series resistor 24 and a second shunt capacitor 26 are connected across capacitor 22, and a second resistor 28 is connected across capacitor 26. Resistors 20 and 24 are bypassed by a diode 30 polarized oppositely to source 14. The fast keying circuit FKC (C is comprised of a shunt resistor 33, and series resistor 34, across which are parallel-connected shunt capacitor 36 and shunt resistor 38. The chifi' keying circuit CKC (C is fed by diode 83, polarized in conducting relationship with source 14, and is composed of series-connected resistors 40 and 42 to ground, capacitors 44 and 46 connected in series and across resistor 42, and a diode 48 connected across capacitor 46 to ground and polarized oppositely to source 14. At point 49 there are also a load resistor 51 to ground and a shunt connection through resistor 50 to a second DC source 52.

The output lead 56 of SKC (C carries the slow starting DC keying voltage to the C photocell pair on two 8 arrays, two photocell pairs being schematically illustrated at 58 and 60. Output lead 56 also is connected to cell 68 via diode 66.

A portion of a typical photocell array is shown pictorially in FIG. 4, wherein a glass substrate 51 (for mounting on stationary disc 11a of FIG. 1) has deposited thereon a metallic circuit pattern composed of the interdigitated portions 13, 15, 17 which respectively comprise the keying electrode 13 and two collection electrodes on one photocell pair as described in FIG. 1. The photosensitive material comprising the strip 19 is deposited, as shown, on the metallic pattern composed of electrodes l3, l5, 17, etc. As described in detail in the aforementioned Jones and Jones et al. patents, the resistance of the deposit 19 between electrode 13 and its neighbors l5 and 17 is varied by modulated illumination produced by rotating over variable-area waveform patterns, not shown. Keying voltage is supplied to electrode 13 via a lead 61, while modulated signal will be collected from electrodes and 17 by leads 63 and 65, respectively.

Referring again to FIG. 3, the output signals from photocells 58, 60 and 68 are passed to opposite terminals of the primary windings of DC-cancelling transformers 62, 64 and 70, respectively, the center taps of which are grounded. The secondary coils of the transformers are connected at one end to ground and at the other end, via stop control switches 72, 74, and 76, respectively, to a common output lead 78 feeding an output amplifier 80 and loudspeaker 82, the latter being representative of any suitable, conventional, electroacoustic-translating system. The output lead 56 of the slow keying circuit can also be connected, as at point 84, to photocell pairs C, and C in 4 and l6 photocell arrays, respectively, in the event that it is desired to actuate such cells from the slow keying circuit. Also, there is shown a connection at point 86, via diode 88, to chiff keying circuit for the note 8;. This means that the pitch corresponding to the note C would be proper to accompany a B note in order to provide a chiff component, as will be explained in detail hereinafter in connection with CKC (C,).

In operation, when key switch 12 (FIG. 3) is actuated by depression of key 10, DC voltage from source 14 is applied across resistors 16 and 18 in series. The potential across resistor 18 in SKC is applied to capacitor 22 via resistor 20, and the voltage across capacitor 22 builds up slowly. This voltage is applied to capacitor 26 via resistor 24. The comparatively slowly rising voltage at the output lead 56 is applied to the cells connected thereto and the voltage drop produced in the cells is modulated by the varying light energy impinging upon them. The alternating components of the tone signals from the two parts of each photocell pair are additive in a center tapped transformer, because the waveform patterns, as at 5 and 7 in H6. 1, are purposely disposed l80 out-of-phase. On the other hand, the DC component from each portion of a photocell pair oppose each other in the grounded center tap primary winding of each transformer and thus cancel. Upon opening of key switch 12, the decay time of the control voltage on lead 56 and hence of the tone signals is hastened by the presence of diode 30 and comparatively low resistor 18 which act to discharge capacitor 26 rather than relatively high rcsistor 28 above.

The output lead 90 from fast keying circuit FKC (C is connected to two 8 cells 92 and 94 and to a 2' cell (not shown) representing note C There is also shown a connection via diode 96 to an Orchestral Flute (4') cell (not shown) corresponding to note C The operation of the fast keying circuit F KC (C is simpler than that of the slow keying circuit in that there is only one RC section composed of series resistor 34 and shunt capacitor 36, the latter of which is charged via resistor 34 from the DC source 14 upon actuation of switch 12. The rate of charge of capacitor 36 is dependent upon the time constant of the capacitor in combination with the Thevenin equivalent resistance of resistor 34 in parallel with resistor 38 and the photocell loads. The voltage drop appearing across resistor 38 is applied to output lead to energize the photocells connected thereto. The buildup and decay rates of circuit FKC (C are relatively fast compared with the slow keying circuit SKC (C During decay, resistor 33 speeds the rate of discharge of capacitor 36.

The chiff keying circuit CKC (C which is the subject of the present invention provides the proper DC keying voltage to produce both a rapidly rising and rapidly decaying tone control envelope, even though key switch 12 is held closed. The photocell actuated by such a pulsed envelope produces a characteristic chiff sound at the beginning of any tone requiring a chiff component. The output lead 98 of the chiff keying circuit is connected via point 100 and a diode 54 to a chiff photocell pair corresponding to the note F This produces a pitch which is somewhat greater than five times the fundamental frequency of a note corresponding to C it is known in the art that such a frequency relationship exists between the main chiff component and the fundamental component of the tones of certain stops, notably stopped flutes. The chiff keying circuit output lead 98 is also connected, via a scaling voltage divider (comprising resistors R, and R,.) and diodes 102 and 103, to a G #8 Diapason photocell pair and to the F Diapason cell pair, respectively, to supply other characteristically high chiff components required. Output lead 98 also has a connection to diode 104, which is connected to the 4' Orchestral Flute photocell pair 106 for note C (From this point there is also a diode 108 connected to the fast keying circuitry (not shown) associated with the same cell pair for note C Thus the 4 Orchestral Flute tone corresponding to the playing key 10 for C, has a fast-starting, steady-state component supplied by the C cell via diode 96, with a subharmonic chiff component (at the C pitch) via diode 104.

The operation of the chiff keying circuit CKC (C,) is more involved than that of the previously described keying circuits. Initially, with key switch 12 open, diode 48 is turned on clamping point 49 to a slightly negative level (the drop across diode 48) and cutting off diode 54. However, when the key switch 12 is closed, the voltage at point 49 becomes positive as capacitors 44 and 46 commence charging via resistor 40. This voltage level at point 49, determined in part by the voltage division between resistors 40 and 51, is sufficiently positive to cut off diode 48 and turn on diode 54, thereby gating on chiff photocell F and all of the cells connected to output lead 98. These cells are thus able to produce tone signals depending upon the rate at which they are modulated by light energy impinging thereon, as explained hereinbefore. Capacitor 44. charges quickly after which source 52 regains control clamping the voltage at point 49 to a slightly negative voltage level, equal to the forward drop across diode 48. The momentary chiff components thus decay even though key switch 12 is held closed. When key switch 12 is opened, capacitor 44 rapidly discharges through resistor 42 and diode 48, and the circuit is reset" for another actuation of key switch 12. A chiff tone is not elicited when key switch 12 is opened because point 49 remains clamped slightly negative as explained above.

The fifth-partial chifi effect can be turned on or off by the organist via chiff tone color stop switch 79. However, the other chiff components are always on" as factory-voiced components of the Diapason 8' and the Orchestral Flute 4' stops, as illustrated in FIG. 3. These can be switched along with their respective steady-state tones by tone-color stop switches 76 and 81 respectively.

If it is desired to excite a given chiff photocell by more than one key (in higher ranges, above C pitch discrimination is not too critical so that two or more adjacent notes may use the same chiff frequency), isolating diodes 83 and 85 must be inserted at the input terminal for each commonly used CKC circuit.

A second key 110 of the same keyboard which contains key actuates a second key switch 112 corresponding to the note C It in turn transmits DC from the source 14 to three keying circuits represented in block form at 114, 116, and I18, which may be similar in characteristics to the keying circuits already illustrated in detail. The outputs of the respective keying circuits 114, 116 and 118 are shown connected similarly to photocells as the outputs of the hereinbefore-described outputs 98, 90 and 56. it is not believed necessary to describe this circuitry in detail.

Thus, it will be seen that there has been presented herein novel chifi' circuit means suitable for use in keyed photocell organs and the like.

While we have described and illustrated one specific embodiment of our invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention .as defined in the appended claims.

We claim:

1. In an electronic musical instrument, the combination comprising:

a first direct current actuable means for producing steadystate tone signals,

a second direct current actuable means for producing chiff tone signals,

a first direct current source,

a key switch,

a steady-state tone envelope-control network,

a chiff-tone envelope-control network,

a first circuit path connectingsaid direct current source via said key switch to the series combination of steady-state tone envelope-control network and said first direct current actuable means,

a second circuit path from said key switch to the series combination of said chiff-tone envelope-control network and said second direct-current actuable means, said chiff-tone envelope-control network comprising:

an input point,

a first resistor,

a second resistor in series with said first resistor between said input point and a common return path,

a first capacitor connected to the junction between said resistors,

a second capacitor in series between said first capacitor and said common return path,

a diode connected between said common return path and the junction between said capacitors,

a second direct-current source,

a third resistor connected between said last-mentioned junction and said second direct current source, said diode being poled so as to be forward-biased by said second direct current source, and

an output system coupled to both said direct current actuable means for converting signals produced therein to sound.

2. In a photoelectric organ having a first direct current source, a plurality of key switches, a first plurality of photocells corresponding to steady-state tones and a second plurality of photocells corresponding to chiff tones, the combination comprising:

a plurality of tone-envelope-control networks,

a plurality of chiff-envelope-control networks, and

a first plurality of circuit paths eachconnecting said directcurrent source via one of said key switches to the series combination of one of said tone-envelope-control networks and one of said first plurality of photocells,

a second plurality of circuit paths from said one of said key switches to the series combination of one of said chiff-envelope-control networks and one of said second plurality of photocells, said chiff-envelope-control network comprising:

an input point,

a first resistor,

source, at least two key switches, an output system and a common chiff photocell coupled to said output system, the combination comprising:

a chifi-envelopecontrol network between said switches and said chiff photocell,

and a pair of diodes coupled respectively between said key switches and said chiff-envelope-control network, said diodes being poled for conduction from said first direct current source upon closure of said key switches, said chiff-envelope-control network comprising:

an input point,

a first resistor,

a second resistor in series with said first resistor between said input point and a common return path,

a first capacitor having a connection with the junction between said resistors,

a second capacitor in series between said first capacitor and said common return path,

a diode connected between said common return path and the junction between said capacitors,

a second direct current source,

a third resistor connected between said last-mentioned junction and said second direct current source, said diode being poled so as to be forward-biased by said second direct current source and an output system coupled between junction of said capacitors and said photocells for converting signals generated therein to musical tones.

4. In an electrical musical instrument of the type in which actuation of each of a plurality of keys causes a corresponding tone to sound:

a plurality of tone signal sources, each of the type wherein wave energy periodically impinges upon an energyresponsive element which is keyable by application of keying signal thereto to provide a tone signal having the wave shape and periodicity of the impinging wave energy and having an amplitude which varies with the applied keying signal amplitude, the tone signal of at least one of said tone signal sources having the frequency and wave shape required to produce chiff effects in the sounding of a tone from another of said tone signal sources;

a first source of DC voltage;

first timing circuit means responsive to application of voltage thereto from said first source of DC voltage for applying a first keying signal to the energy-responsive element of said another of said tone signal sources, said first keying signal rising to a steady amplitude within a predetermined time interval;

second timing circuit means responsive to application of voltage thereto from said first source of DC voltage for applying a second keying signal to the energy-responsive element of said one of said tone signal sources, said second keying signal comprising a signal pulse having a rise time which is significantly shorter than said predetermined time interval, said pulse immediately beginning to decay upon completing its rise; and

at least one key switch operative in response to actuation of one of said keys for concurrently applying voltage from said first source to said first and second timing circuit means.

5. The combination according to claim 3 wherein said second timing circuit means comprises:

an input terminal for receiving voltage from said first source upon operation of said key switch,

an output terminal for conducting said second keying signal to said energy-responsive element of said one of said tone signal sources;

a second source of DC voltage;

a common return path for said first and second sources;

a first resistor and first capacitor connected in series between said input and output terminals;

a second resistor connected in series with said second source between said output terminal and said common return path, said second source being polarized to conduct current relative to said output terminal in a direction opposite that of said first source;

a diode connected between said output terminal and said common return path and polarized to conduct current in circuit with said second source; and

resistive discharge path means for discharging said first capacitor to said common return path in the absence of voltage from said first source at said input terminal;

whereby, upon application of voltage from said first source to said input terminal the voltage at said output terminal jumps to a peak value and then decays as said first capacitor commences charging.

6. The combination according to claim 3 further comprisat least a second key switch operative in response to actuation of another of said keys for applying voltage from said first source to said second keying circuit.

7. In an electronic organ, a chiff keying circuit responsive to application of voltage thereto from a first source of DC voltage for providing an output pulse which rises quickly to a peak amplitude and thereupon immediately begins decaying from said peak amplitude, said circuit comprising:

an input terminal;

switch means for selectively applying voltage from said first source to said input terminal;

an output terminal;

a second source of DC voltage;

a common return path for said first and second sources;

a first resistor and first capacitor connected in series between said input and output terminals;

a second resistor connected in series with said second source between said output terminal and said common return path, said second source being polarized to conduct current relative to said output terminal in a direction opposite that of said first source;

a clamping diode connected between said output terminal and said common return path, and polarized to conduct current from said second source; and

a resistive discharge path for discharging said first capacitor through said common return path in the absence of voltage from said first source at said input terminal.

8. ln an electronic organ, a chiff keying network comprising, a timing resistance, a source of voltage having a terminal at reference control, a key switch connected between said source of voltage and said timing resistance, a first capacitor in series with said timing resistance, a second capacitor connected between said first capacitor and a point of reference potential, a first diode connected in shunt to second capacitor poled to be nonconductive in response to said voltage connected across only said second capacitor, means for clamping the potential across said diode to a preset value, said clamping means connected to junction of first and second capacitors and a load resistance connected in shunt to said diode, a photoresistor having a keying electrode and a diode poled to be conductive of said voltage connected in series between said load resistance and said keying electrode. 

1. In an electronic musical instrument, the combination comprising: a first direct current actuable means for producing steady-state tone signals, a second direct current actuabLe means for producing chiff tone signals, a first direct current source, a key switch, a steady-state tone envelope-control network, a chiff-tone envelope-control network, a first circuit path connecting said direct current source via said key switch to the series combination of steady-state tone envelope-control network and said first direct current actuable means, a second circuit path from said key switch to the series combination of said chiff-tone envelope-control network and said second direct-current actuable means, said chiff-tone envelope-control network comprising: an input point, a first resistor, a second resistor in series with said first resistor between said input point and a common return path, a first capacitor connected to the junction between said resistors, a second capacitor in series between said first capacitor and said common return path, a diode connected between said common return path and the junction between said capacitors, a second direct-current source, a third resistor connected between said last-mentioned junction and said second direct current source, said diode being poled so as to be forward-biased by said second direct current source, and an output system coupled to both said direct current actuable means for converting signals produced therein to sound.
 2. In a photoelectric organ having a first direct current source, a plurality of key switches, a first plurality of photocells corresponding to steady-state tones and a second plurality of photocells corresponding to chiff tones, the combination comprising: a plurality of tone-envelope-control networks, a plurality of chiff-envelope-control networks, and a first plurality of circuit paths each connecting said direct-current source via one of said key switches to the series combination of one of said tone-envelope-control networks and one of said first plurality of photocells, a second plurality of circuit paths from said one of said key switches to the series combination of one of said chiff-envelope-control networks and one of said second plurality of photocells, said chiff-envelope-control network comprising: an input point, a first resistor, a second resistor in series with said first resistor between said input point and a common return path, a first capacitor having a connection with the junction between said resistors, a second capacitor in series between said first capacitor and said common return path, a diode connected between said common return path and the junction between said capacitors, a second direct current source,
 3. In a keyed-photocell organ having a first direct current source, at least two key switches, an output system and a common chiff photocell coupled to said output system, the combination comprising: a chiff-envelope-control network between said switches and said chiff photocell, and a pair of diodes coupled respectively between said key switches and said chiff-envelope-control network, said diodes being poled for conduction from said first direct current source upon closure of said key switches, said chiff-envelope-control network comprising: an input point, a first resistor, a second resistor in series with said first resistor between said input point and a common return path, a first capacitor having a connection with the junction between said resistors, a second capacitor in series between said first capacitor and said common return path, a diode connected between said common return path and the junction between said capacitors, a second direct current source, a third resistor connected between said last-mentioned junction and said second direct current source, said diode being poled so as to be forward-biased by said second direct current source and an output system coupled between junction of said capacitors and said photocells for converting signals generated therein to musical tones.
 4. In an electrical musical instrument of the type in which actuation of each of a plurality of keys causes a corresponding tone to sound: a plurality of tone signal sources, each of the type wherein wave energy periodically impinges upon an energy-responsive element which is keyable by application of keying signal thereto to provide a tone signal having the wave shape and periodicity of the impinging wave energy and having an amplitude which varies with the applied keying signal amplitude, the tone signal of at least one of said tone signal sources having the frequency and wave shape required to produce chiff effects in the sounding of a tone from another of said tone signal sources; a first source of DC voltage; first timing circuit means responsive to application of voltage thereto from said first source of DC voltage for applying a first keying signal to the energy-responsive element of said another of said tone signal sources, said first keying signal rising to a steady amplitude within a predetermined time interval; second timing circuit means responsive to application of voltage thereto from said first source of DC voltage for applying a second keying signal to the energy-responsive element of said one of said tone signal sources, said second keying signal comprising a signal pulse having a rise time which is significantly shorter than said predetermined time interval, said pulse immediately beginning to decay upon completing its rise; and at least one key switch operative in response to actuation of one of said keys for concurrently applying voltage from said first source to said first and second timing circuit means.
 5. The combination according to claim 3 wherein said second timing circuit means comprises: an input terminal for receiving voltage from said first source upon operation of said key switch, an output terminal for conducting said second keying signal to said energy-responsive element of said one of said tone signal sources; a second source of DC voltage; a common return path for said first and second sources; a first resistor and first capacitor connected in series between said input and output terminals; a second resistor connected in series with said second source between said output terminal and said common return path, said second source being polarized to conduct current relative to said output terminal in a direction opposite that of said first source; a diode connected between said output terminal and said common return path and polarized to conduct current in circuit with said second source; and resistive discharge path means for discharging said first capacitor to said common return path in the absence of voltage from said first source at said input terminal; whereby, upon application of voltage from said first source to said input terminal the voltage at said output terminal jumps to a peak value and then decays as said first capacitor commences charging.
 6. The combination according to claim 3 further comprising: at least a second key switch operative in response to actuation of another of said keys for applying voltage from said first source to said second keying circuit.
 7. In an electronic organ, a chiff keying circuit responsive to application of voltage thereto from a first source of DC voltage for providing an output pulse which rises quickly to a peak amplitude and thereupon immediately begins decaying from said peak amplitude, said circuit comprising: an input terminal; switch means for selectively applying voltage from said first source to said input terminal; an output terminal; a second source of DC voltage; a common return path for said first and second sources; a first resistor and first capacitor connected in series between said input and output terminals; a second resistor connected in series with said second source between said output terminal and said common retUrn path, said second source being polarized to conduct current relative to said output terminal in a direction opposite that of said first source; a clamping diode connected between said output terminal and said common return path, and polarized to conduct current from said second source; and a resistive discharge path for discharging said first capacitor through said common return path in the absence of voltage from said first source at said input terminal.
 8. In an electronic organ, a chiff keying network comprising, a timing resistance, a source of voltage having a terminal at reference control, a key switch connected between said source of voltage and said timing resistance, a first capacitor in series with said timing resistance, a second capacitor connected between said first capacitor and a point of reference potential, a first diode connected in shunt to second capacitor poled to be nonconductive in response to said voltage connected across only said second capacitor, means for clamping the potential across said diode to a preset value, said clamping means connected to junction of first and second capacitors and a load resistance connected in shunt to said diode, a photoresistor having a keying electrode and a diode poled to be conductive of said voltage connected in series between said load resistance and said keying electrode. 